In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.
An example of applications available in some communications system is group communications services. In general terms, group communication means that the same information or media is delivered to multiple client nodes. In group communication systems (e.g., Push-To-Talk (PTT) systems) the client nodes receiving the same media constitute a group of client nodes. These client nodes may be located at different locations. If many client nodes are located within the same area, multicast or broadcast based transmission using e.g., Multicast-Broadcast Multimedia Services (MBMS) is efficient for communications to the group of client nodes, because communications resources such as time and frequency resources are shared among client nodes. If client nodes are spread out over a large geographical area it can be more efficient to use unicast transmission for communications to the group of client nodes. However, even if MBMS-based transmission is preferred, there may not be sufficient MBMS resources available to serve all groups of client nodes. Some client nodes and groups thereof may then be served using unicast transmission.
When using MBMS to broadcast media in a group communications system, the transmitting client node uses unicast transmission to transmit the media to the group communications system, and a control node in the group communications system uses broadcast-based transmission to send the media to client nodes participating in the group communication.
When Mobile Terminated (MT) traffic (i.e., traffic terminated at one of the client nodes) is initiated to a client node that is in an idle mode (e.g., radio resource control (RRC) idle in the Long Term Evolution (LTE) suite of telecommunications standards) the client node is normally asleep and only listens periodically for paging information (e.g. to the Physical Downlink Control Channel (PDCCH) in LTE). If there is a paging message the client node would demodulate the paging channel (denoted PCH in LTE). The paging cycle can be set to between 320 to 2560 ms. This means that when the paging cycle is 320 ms, the average wake up time for the client node is 160 ms depending on when the traffic arrives in relation to the paging cycle. On top of this it takes approximately 100 ms to change state on the client node from idle mode to connected mode.
Such delay is an issue in some communication scenarios, for instance when broadcast-based transmission is used in delay-critical applications.
For real time applications such as, but not limited to, PTT, this can impact the call setup and mouth-to-ear delay if the PTT system is using unicast transmission and some of the receiving client nodes are in idle mode. Potentially packets may also be dropped until the client nodes reach connected mode and re-establishes a radio bearer (RAB).
Hence, there is still a need for an improved handling of real time critical services, such as PTT, in a group communications system.